For a wash process of a washing machine, the water level in the tub may be set based on the size of a laundry load and, sometimes, the fabric type of the laundry load, if this information is available. From a cost of the washing machine perspective, it is better to have the user manually input the laundry load information through a user interface; although from the perspective of convenience to the user, it may be desirable to have the washing machine automatically determine the information. From an accuracy perspective, manual input by the user often is a greater source of error because the user may often overestimate or underestimate the load size, thereby resulting in too much or too little water, respectively, for the wash process. Too much water is wasteful, and too little water may lead to an insufficient wash performance and/or other negative implications. Users have also been known to forget to enter the information. The automatic determination by the machine is often more consistent and accurate than the manual entry by the user.
Many methods are known for the washing machine to automatically determine the load size and/or fabric type, such as by employing an output of the motor that drives the drum within the tub and the agitator within the drum. However, these systems depend on additional motor sensors, such as motor torque, and the associated hardware, such as multiple or variable speed motors, and their electronics, such as the motor controller, which naturally increase the cost of the machine. These associated additional costs are often unacceptable, especially in machines that use single speed motors and simple controls. Therefore, many machines have motors that do not provide output useful for determining load size or have other limitations that preclude or make undesirable known methods for automatically determining load size.